JP7255407B2 - Spark plug manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing a spark plug.

Patent Document 1 discloses a method of manufacturing a spark plug containing a resistor. In the spark plug manufacturing method of Patent Document 1, first, the center electrode is inserted into the shaft hole of the insulator. Next, the axial hole is filled with the first conductive glass powder, the resistor composition powder for forming the resistor, and the second conductive glass powder, and the terminal fitting is inserted.

Next, the powder filled in the axial hole of these insulators is heated and softened, and the terminal fitting is pressed toward the tip side (that is, the center electrode side) by hot pressing. Then, these softened powders are solidified by cooling, and the first seal layer as a sintered body, the resistor, and the second seal are placed between the center electrode and the terminal fitting in the shaft hole of the insulator. Layers are formed in this order from the tip side.

JP 2010-135345 A

However, in the spark plug disclosed in Patent Literature 1, it is conceivable that the insulator is charged due to friction generated during transportation of the insulator alone. Thus, in the case of manufacturing a spark plug using a charged insulator, when the first conductive glass powder for forming the first seal layer is filled in the shaft hole of the insulator, the conductive It is conceivable that part of the glass powder is electrically adsorbed to the inner wall of the insulator. In that case, after sintering, the peripheral edge of the base end face of the first seal layer may be formed so as to rise greatly toward the base end side.

If the peripheral edge of the base end surface of the first seal layer is formed so as to rise greatly toward the base end side, the peripheral edge of the base end surface of the first seal layer and the resistor will be locally close to each other, and a desired resistance value cannot be obtained. case is conceivable. That is, in the spark plug manufacturing method described in Patent Document 1, the resistance values of manufactured spark plugs are not stable among products, and individual differences in resistance values tend to increase.

The present invention has been made in view of this problem, and is intended to suppress the peripheral edge of the base end surface of the first sealing layer formed by sintering the first conductive glass powder from creeping up significantly toward the base end. The object of the present invention is to provide a method for manufacturing a spark plug capable of

One aspect of the present invention is a method of manufacturing a spark plug (1) containing a resistor (8), comprising:
an electrode placement step of placing the center electrode (3) in the axial hole (21) of the insulator (2);
a first filling step of filling a base end side of the center electrode in the axial hole with a first conductive glass powder (41a);
a second filling step of filling a base end side of the first conductive glass powder in the axial hole with a resistor composition powder (8a) for forming the resistor;
a third filling step of filling a second conductive glass powder (42a) on the base end side of the resistor composition powder in the axial hole;
a sintering step of sintering the first conductive glass powder, the resistor composition powder, and the second conductive glass powder, which are filled in the axial hole;
Prior to the second filling step, at least one of the insulator and the first conductive glass powder is brought into a non-charged state, or the insulator and the first conductive glass powder are charged. A method for manufacturing a spark plug, including a charge conditioning step for aligning a state with a spark plug.

In the spark plug manufacturing method of the above aspect, before the second filling step of filling the resistor composition powder into the shaft hole, at least one of the insulator and the conductive glass is brought into a non-charged state, or It includes a charge adjustment process for matching the charged states of the insulator and the conductive glass. Therefore, after the charge adjustment step and before filling the resistor composition powder into the axial hole, the insulator and the conductive glass powder are charged to opposite polarities, and therefore, the conductive glass powder It is possible to prevent the portion from being electrically attracted to the inner surface of the insulator. As a result, in the manufactured spark plug, it is possible to prevent the peripheral edge of the base end surface of the first seal layer from being formed so as to largely creep up toward the base end side.

As described above, according to the above aspect, the spark plug is capable of suppressing the peripheral edge of the base end surface of the first sealing layer formed by sintering the first conductive glass powder from creeping up greatly toward the base end. A manufacturing method can be provided.
It should be noted that the symbols in parentheses described in the claims and the means for solving the problems indicate the corresponding relationship with the specific means described in the embodiments described later, and limit the technical scope of the present invention. not a thing

FIG. 2 is a cross-sectional view including the central axis of the spark plug in Embodiment 1; FIG. 4 is a cross-sectional view for explaining a method of manufacturing a spark plug in Embodiment 1; 2 is an enlarged cross-sectional view of the spark plug around the resistor in Embodiment 1. FIG. FIG. 4 is an enlarged cross-sectional view of a spark plug around a resistor in a reference embodiment;

(Embodiment 1)
An embodiment of a method for manufacturing the spark plug 1 will be described with reference to FIGS. 1 to 3. FIG.
The method of manufacturing the spark plug 1 of this embodiment is a method of manufacturing the spark plug 1 containing the resistor 8 . First, the structure of the spark plug 1 obtained by the manufacturing method of this embodiment will be described with reference to FIG. In this specification, the direction in which the central axis of the spark plug 1 extends is referred to as the plug axial direction X, and the side where the center electrode 3 protrudes from the insulator 2 on one side of the plug axial direction X is the tip end. side, and the opposite side is called the proximal side.

A spark plug 1 includes a cylindrical housing 6, a cylindrical insulator 2 held inside the housing 6, a center electrode 3 disposed inside the insulator 2, a first sealing layer 41, and a resistor 8. , a second seal layer 42 and a terminal fitting 5 .

The insulator 2 is made of, for example, a ceramic sintered body obtained by molding an insulating ceramic material such as alumina into a predetermined shape and then firing the molded material. The insulator 2 has a shaft hole 21 formed so as to penetrate in the axial direction X of the plug through a central portion thereof when viewed in the axial direction X of the plug. The shaft hole 21 has a small diameter portion 211, a stepped portion 212, and a large diameter portion 213 from the tip side.

The small diameter portion 211 and the large diameter portion 213 have a constant inner diameter in the axial direction X of the plug. The large diameter portion 213 has a larger inner diameter than the small diameter portion 211 . The stepped portion 212 is formed so as to connect the small diameter portion 211 and the large diameter portion 213, and is formed in a tapered shape that increases in diameter toward the base end side.

The inner diameter of the large diameter portion 213 is 3.8 mm or less. In consideration of the rigidity and electrical resistance of the insulator 2, this is the maximum inner diameter of the large diameter portion 213 that can be formed in the insulator 2 that can be assembled in the housing 6 that has a mounting screw portion 61 with a screw diameter of M12 or less, which will be described later. and falls into the category of spark plugs in which the inner diameter of the large-diameter portion 213 is relatively small. In recent years, as the efficiency and output of engines have increased, there has been an increasing need for smaller diameter spark plugs to ensure greater freedom in engine design. A reduction in the diameter of the insulator 2 and thus a reduction in the diameter of the shaft hole 21 are required.

A center electrode 3 , a first sealing layer 41 , a resistor 8 , a second sealing layer 42 and a terminal fitting 5 are arranged in the axial hole 21 in this order from the tip side. The center electrode 3 is formed in a rod shape, and has its distal end protruding from the shaft hole 21 . A base end portion 31 of the center electrode 3 is supported by a stepped portion 212 of the shaft hole 21 , thereby positioning the center electrode 3 within the shaft hole 21 . A first seal layer 41, a resistor 8, and a second seal layer 42 are arranged in this order from the tip side on the base end side (that is, the large diameter portion 213) of the center electrode 3 in the shaft hole 21. .

The first sealing layer 41 is made of a sintered body of first conductive glass powder, which is obtained by mixing metal powder such as copper powder into glass. The first seal layer 41 is in close contact with the inner wall surface of the shaft hole 21 to ensure airtightness within the shaft hole 21 . The first sealing layer 41 is in contact with the center electrode 3 at its distal end and in contact with the resistor 8 at its proximal end. Conducting.

The resistor 8 is made of a sintered body obtained by sintering a resistor composition powder obtained by mixing a resistor material powder such as carbon into glass. Resistor 8 is for suppressing transmission of radio noise caused by spark discharge of spark plug 1 to the outside of spark plug 1 . The resistivity of the resistor 8 in the plug axial direction X is greater than the resistivity of each of the first sealing layer 41 and the second sealing layer 42 .

The second seal layer 42 is made of a sintered body of second conductive glass powder. Like the first conductive glass powder, the second conductive glass powder is made of copper glass powder (that is, glass mixed with metal powder such as copper powder). The second seal layer 42 is in close contact with the inner wall surface of the large-diameter portion 213 of the shaft hole 21 to ensure airtightness within the shaft hole 21 . The second sealing layer 42 is in contact with the resistor 8 at its distal end and in contact with the terminal fitting 5 at its proximal end, and the resistor 8 and the terminal fitting 5 are connected via the second sealing layer 42. Conducting.

Boundary lines between the first seal layer 41 and the resistor 8 and between the resistor 8 and the second seal layer 42 can be confirmed in a cross section including the central axis of the spark plug 1 . A terminal fitting 5 is arranged in the shaft hole 21 so as to be adjacent to the base end side of the second seal layer 42 .

The terminal fitting 5 is electrically connected to the center electrode 3 via the second seal layer 42 , the resistor 8 and the first seal layer 41 . The terminal fitting 5 has an insertion terminal portion 51 inserted into the shaft hole 21 and a protruding terminal portion 52 protruding from the shaft hole 21 to the base end side. A second seal layer 42 is in close contact with the distal end portion of the insertion terminal portion 51 . A tip portion of the insertion terminal portion 51 is threaded to improve adhesion with the second seal layer 42 . The outer diameter of the insertion terminal portion 51 is smaller than the inner diameter of the shaft hole 21 , and the second sealing layer 42 is also arranged between the tip portion of the insertion terminal portion 51 and the shaft hole 21 . The projecting terminal portion 52 is a terminal for connecting the spark plug 1 to the ignition coil.

The insulator 2 is held by the housing 6 . The housing 6 is made of a heat-resistant metal material such as an iron-based alloy and formed into a cylindrical shape. A mounting threaded portion 61 is formed on the outer peripheral portion of the housing 6 for screwing the housing 6 into a female threaded hole provided in a plug hole of a cylinder head of an internal combustion engine.

A ground electrode 7 is connected to the tip of the housing 6 . The ground electrode 7 faces the center electrode 3 in the axial direction X of the plug, and forms a discharge gap G between the ground electrode 7 and the center electrode 3 in the axial direction X of the plug. By applying a high voltage to the center electrode 3, spark discharge is generated in the discharge gap G, and the air-fuel mixture in the combustion chamber is ignited.

Next, a method for manufacturing the spark plug 1 of this embodiment will be described with reference to FIG.
In this embodiment, a method of forming the center electrode 3, the first seal layer 41, the resistor 8, the second seal layer 42, and the terminal fitting 5 inside the insulator 2 will be described.

First, as shown in FIG. 2(a), a preparatory step is performed to prepare an insulator 2 manufactured at a place different from the place where the present method is carried out, for example. Here, there is concern that the insulator 2 is in a charged state due to friction or the like that occurs during transportation from the place where it was manufactured. Therefore, after the preparation process, the charge adjustment process shown in FIG. 2B is performed.

The charge adjustment process is a process for preventing the insulator 2 and the first conductive glass powder from being charged with opposite polarities. As shown in FIG. 2(b), in the present embodiment, the charge adjustment step is a step of neutralizing the insulator 2 so as to bring the insulator 2 into a non-charged state. A static elimination device 11 is used to eliminate static electricity from the insulator 2 . As the static eliminator 11, it is possible to adopt a device that has a needle-like electrode and generates ions around the electrode by applying a voltage to the needle-like electrode. Furthermore, as the static eliminator 11, the generated ions can be diffused by the air A. FIG.

As the static eliminator 11, for example, a known pulse AC type, AC type, DC type, or pulse DC type ionizer can be adopted. By using these static eliminators 11, it is easy to quickly neutralize the charge amount of the insulator 2 to near 0 nC (nanocoulomb). It should be noted that it is also possible to employ other methods as the method of static elimination.

Static elimination is performed on the inner wall of the shaft hole 21 of the insulator 2 . That is, by blowing ions generated by the static eliminator 11 into the shaft hole 21 with the air A, static elimination of the insulator 2 is performed. The charge adjustment process is performed on the single insulator 2 to which other members such as the center electrode 3 are not assembled. As a result, the air A can be blown to the inside of the insulator 2 so as to pass through the shaft hole 21, and the static elimination of the insulator 2 can be facilitated. After the charge adjustment process, the electrode placement process is performed as shown in FIG. 2(c).

As shown in FIG. 2(c), in the electrode placement step, the center electrode 3 is inserted into the shaft hole 21 of the insulator 2 from the base end side of the shaft hole 21 for placement. Here, the center electrode 3 is held in the shaft hole 21 by supporting the base end portion 31 of the center electrode 3 on the stepped portion of the shaft hole 21 (see reference numeral 212 in FIG. 2B). Then, as shown in FIG. 2(d), the first filling step is performed.

As shown in FIG. 2(d), in the first filling step, first conductive glass powder 41a (copper glass powder). At this time, the insulator 2 is in a non-charged state due to the charge adjustment process, so the first conductive glass powder 41 a is not electrically attracted into the shaft hole 21 of the insulator 2 .

Then, a rod-shaped jig (not shown) is inserted into the shaft hole 21 to press the first conductive glass powder 41a toward the tip side. The jig is formed to have a diameter slightly smaller than the inner diameter of the portion of the shaft hole 21 where the first conductive glass powder 41a is arranged so that it can be inserted into the shaft hole 21 . In the spark plug manufacturing method that does not include the charge adjustment step, unlike the method of the present embodiment, if part of the conductive glass powder is electrically adsorbed in the shaft hole, the jig is inserted into the shaft hole. Even if it is inserted, the conductive glass powder adsorbed to the axial hole cannot be removed.

In this embodiment, after pressing the first conductive glass powder 41a with a jig, the second filling step is performed as shown in FIG. 2(e).

As shown in FIG. 2(e), in the second filling step, the base end side of the first conductive glass powder 41a in the shaft hole 21 is filled with the resistor composition powder 8a for forming the resistor 8. It is a process. Then, a jig (not shown) is inserted into the shaft hole 21 to press the resistor composition powder 8a toward the tip side. Then, as shown in FIG. 2(f), the third filling step is performed.

As shown in FIG. 2(f), the third filling step is a step of filling the base end side of the resistor composition powder 8a in the shaft hole 21 with the second conductive glass powder 42a. Then, a jig (not shown) is inserted into the shaft hole 21 to press the second conductive glass powder 42a toward the tip side. As described above, the first conductive glass powder 41a, the resistor composition powder 8a, and the second conductive glass powder 42a are layered in this order on the base end side of the center electrode 3 in the shaft hole 21 .

After the third filling step, the terminal fitting 5 is inserted into the shaft hole 21 from the base end side of the shaft hole 21 . In this state, the terminal fitting 5 is arranged on the base end side of the final position with respect to the insulator 2 . In the subsequent sintering process, the terminal fitting 5 is pressed toward the tip side and placed in the position when the spark plug 1 is completed.

As shown in FIG. 3(g), the sintering step is a step of sintering the first conductive glass powder 41a, the resistor composition powder 8a and the second conductive glass powder 42a. The sintering process is performed, for example, in the heating furnace 10 at a softening temperature of the glass materials of the first conductive glass powder 41a, the resistor composition powder 8a, and the second conductive glass powder 42a. As a result, the first conductive glass powder 41a, the resistor composition powder 8a, and the second conductive glass powder 42a are softened and become fluid. Then, the terminal fitting 5 is pushed toward the distal end side in a state in which they can flow.

By pushing the terminal fitting 5 toward the tip side, the fluid of the second conductive glass powder 42a also flows into the gap between the insertion terminal portion 51 of the terminal fitting 5 and the shaft hole 21 on the outer peripheral side, and the terminal fitting 5 and the fluid adhesion of the second conductive glass powder 42a is improved. Then, by lowering the temperature in the heating furnace 10, the fluid of the first conductive glass powder 41a, the fluid of the resistor composition powder 8a, and the fluid of the second conductive glass powder 42a are solidified. , a first sealing layer 41, a resistor 8 and a second sealing layer 42 are obtained as shown in FIG. 2(h). That is, the first conductive glass powder 41a is sintered to form the first sealing layer 41, the resistor composition powder 8a is sintered to form the resistor 8, and the second conductive glass powder 42a is sintered. It becomes the second sealing layer 42 .

As schematically shown in FIG. 3, also in the present embodiment, the peripheral edge of the base end surface of the first seal layer 41 is reduced due to the fact that the terminal fitting 5 is pushed toward the tip side of the insulator 2 in the sintering step. , and the peripheral edge of the proximal end face of the resistor 8, a raised portion 100 that slightly rises toward the proximal end side can be formed.
As described above, the center electrode 3 , the first seal layer 41 , the resistor 8 , the second seal layer 42 and the terminal fittings 5 can be formed inside the insulator 2 .

Next, the effects of this embodiment will be described.
The method of manufacturing the spark plug 1 of the present embodiment includes a charge adjustment step of making the insulator 2 uncharged before the second filling step of filling the resistor composition powder 8a into the shaft hole 21 . Therefore, after the charge adjustment step and before filling the resistor composition powder 8a into the axial hole 21, the insulator 2 and the conductive glass powder are charged to opposite polarities, and the conductive glass Part of the powder can be prevented from being electrically adsorbed to the inner surface of the insulator 2 . As a result, in the manufactured spark plug 1, it is possible to prevent the peripheral edge of the base end surface of the first seal layer 41 from being formed so as to largely creep up toward the base end side.

On the other hand, as shown in FIG. 4, unlike the present application, in a spark plug 9 manufactured by a manufacturing method that does not include a charge adjustment process, for example, the first conductive glass that constitutes the first seal layer 41 in the insulator 2 It is conceivable that the insulator 2 is charged before the powder is filled. In this case, when the insulator 2 is filled with the first conductive glass powder, part of the first conductive glass powder is electrically adsorbed in the shaft hole 21 . As a result, in the manufactured spark plug 9 , there is a possibility that the peripheral edge of the base end surface of the first seal layer 41 is formed with a crawl-up portion 900 that is larger than the surroundings and rises toward the base end side. If such a large rising portion is formed, the resistance value between the rising portion in the first seal layer 41 and the second seal layer 42 may locally decrease, and the desired resistance value may not be obtained. can be considered. That is, the resistance value of the manufactured spark plugs 9 is not stable among products, and individual differences in resistance values tend to increase.

Therefore, as in the present embodiment, by performing the charge adjustment process before the second filling process, it is possible to prevent the peripheral edge of the base end surface of the first seal layer 41 from creeping up greatly toward the base end side. It is easy to obtain a stable resistance value between products.

In addition, the charge adjusting step is a step of removing static electricity from at least one of the insulator 2 and the first conductive glass powder 41a so as to be in a non-charged state. Therefore, in the charge adjusting process, it is sufficient to neutralize at least one of the insulator 2 and the first conductive glass powder 41a, which facilitates simplification of the process.

In addition, static elimination of the insulator 2 is performed on the inner wall of the shaft hole 21 of the insulator 2 . Therefore, it is easier to prevent the peripheral edge of the base end surface of the first seal layer 41 from creeping up significantly toward the base end. That is, when the inner wall of the shaft hole 21 of the insulator 2 is charged, when the first conductive glass powder 41a is filled in the shaft hole 21, part of the first conductive glass powder 41a is It becomes easier to electrically stick to the inner wall of the shaft hole 21 . Therefore, by removing the static electricity from the inner wall of the shaft hole 21, the conductive glass powder sticks to the shaft hole 21, and the peripheral edge of the base end surface of the first seal layer 41 of the finished spark plug 1 creeps up greatly toward the base end side. easy to prevent.

Furthermore, the inner diameter of the portion of the shaft hole 21 where the first conductive glass powder 41a is arranged (that is, the large diameter portion 213) is 3.8 mm or less. That is, as described above, the inner diameter of the large-diameter portion 213 is determined in consideration of the rigidity and electrical resistance of the insulator 2. It is equal to or less than the maximum inner diameter of the shaft hole 21 that can be formed. Therefore, the large-diameter portion 213 is formed relatively small, and the diameter of the spark plug 1 can be reduced.

On the other hand, the smaller the large-diameter portion 213, the easier it is for each portion of the conductive glass powder to approach the inner wall of the shaft hole 21 in the first filling step of filling the shaft hole 21 with the first conductive glass powder 41a. In the completed spark plug 1, the peripheral edge of the base end face of the first seal layer 41 is likely to be greatly raised to the base end side. Even in the spark plug 1 where such a concern is high, by performing the charge adjustment process before the second filling process as described above, the peripheral edge of the base end surface of the first seal layer 41 is formed to rise greatly toward the base end side. can be effectively prevented.

As described above, according to the present embodiment, it is possible to provide a method of manufacturing a spark plug that can prevent the peripheral edge of the base end surface of the first seal layer from creeping up to the base end side.

(Embodiment 2)
This embodiment is a form in which the charge adjustment process is changed from the first embodiment.

The electric charge adjustment process of this embodiment is a process of aligning the charged states of the insulator 2 and the first conductive glass powder 41a before the second filling process. For example, in the charge adjustment step, both the inner wall of at least the axial hole 21 of the insulator 2 and the first conductive glass powder 41a are charged positively or negatively.

Others are the same as those of the first embodiment.
Note that, of the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

In this embodiment, before the second filling process, a charge adjustment process is provided to make the charged states of the insulator 2 and the first conductive glass powder 41a uniform. Therefore, a repulsive force acts between the inner wall of the insulator 2 and the first conductive glass powder 41a, and the first conductive glass powder 41a is electrically stuck in the shaft hole 21 in the first filling process. In the completed spark plug 1, it is possible to prevent the peripheral edge of the base end surface of the first seal layer 41 from creeping up greatly toward the base end side.
In addition, it has the same effects as those of the first embodiment.

(Embodiment 3)
This embodiment is a form in which the charge adjustment process is changed from the first and second embodiments.

In the present embodiment, the charge adjustment step is a step in which the insulator 2 is stored in a conductive container, wire mesh, or the like after the insulator 2 is manufactured, and the insulator 2 is not charged in the first place.
Others are the same as those of the first embodiment.

This embodiment also has the same effect as the first embodiment.

The present invention is not limited to the embodiments described above, and can be applied to various embodiments without departing from the scope of the invention.

For example, in the first embodiment, static elimination of the insulator 2 as the charge adjustment step is carried out on the inner wall of the shaft hole 21. However, for example, by blowing air A from the static eliminator 11 to the outside of the insulator 2, the static elimination can be performed. It is also possible to work from outside the insulator 2 . In this case, compared to the case where the inner wall of the shaft hole 21 is directly neutralized, it may take time to neutralize the inner wall of the shaft hole 21, but the insulator 2 can be neutralized from the outside of the insulator 2. Become.

Further, in each of the above-described embodiments, the charge adjusting process is performed before the electrode disposing process of disposing the center electrode 3 in the insulator 2, but the second filling process of filling the resistor composition powder 8a into the axial hole 21 It is not limited to this as long as it is before . For example, the charge adjustment process may be performed immediately after the electrode placement process, or may be performed after the first filling process of filling the first conductive glass powder 41a into the axial hole 21 and before the second filling process. may

Reference Signs List 1 spark plug 2 insulator 21 shaft hole 3 center electrode 41a first conductive glass powder 42a second conductive glass powder 8a resistor composition powder

Claims (4)

A method for manufacturing a spark plug (1) containing a resistor (8), comprising:
an electrode placement step of placing the center electrode (3) in the axial hole (21) of the insulator (2);
a first filling step of filling a base end side of the center electrode in the axial hole with a first conductive glass powder (41a);
a second filling step of filling a base end side of the first conductive glass powder in the axial hole with a resistor composition powder (8a) for forming the resistor;
a third filling step of filling a second conductive glass powder (42a) on the base end side of the resistor composition powder in the axial hole;
a sintering step of sintering the first conductive glass powder, the resistor composition powder, and the second conductive glass powder, which are filled in the axial hole;
Prior to the second filling step, at least one of the insulator and the first conductive glass powder is brought into a non-charged state, or the insulator and the first conductive glass powder are charged. A method of making a spark plug, including a charge conditioning step to align the spark plug. 2. The method of manufacturing a spark plug according to claim 1, wherein said charge adjusting step is a step of removing static electricity from at least one of said insulator and said first conductive glass powder to bring it into a non-charged state. 3. The method of manufacturing a spark plug according to claim 2, wherein the static elimination is performed on the inner wall of the shaft hole of the insulator. 4. The method of manufacturing a spark plug according to claim 1, wherein an inner diameter of a portion of said axial hole where said first conductive glass powder is arranged is 3.8 mm or less.

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